Process of preparation of uranium compounds from uranium-molybdenum alloys



Sept. 28, 965 M. BOURGEOIS ETAL 3,208,815

- PROCESS OF PREPARATION OF URANIUM COMPOUNDS FROM URANIUM-MOLYBDENUM ALLOYS Filed July 10. 1961 4 Sheets-Sheet 1 :r. In 1 a: u -N '6 I O I f N .0

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o ooo oo ooo O o o o o o C) 0 O o 2 o 0) l\ o m w m N INVENTORS M/c/IEL BOI/RG-EO/S PIERRE 54:1 am 5 A TTORNEYS United States Patent 3,208,815 PROCESS OF PREPARATION OF URANIUM This invention relates to the preparation of uranium compounds from uranium-molybdenum alloys.

Among the processes for dry treatment of irradiated nuclear fuels, those based on the separation of uranium hexafluoride are generally preferred and it is particularly advantageous to obtain this latter substance by fluoriding an oxide of uranium such as U0 or U 0 This method is limited, however, to fuel elements based on uranium oxide Or on uranium in an easily oxidizable form, but in the case of uranium-molybdenum alloys, the oxidizing reaction, for example by means of air or oxygen, is diflicult to control, and above a certain molybdenum content it takes place at an appreciable speed only at high temperatures; the reaction at these temperatures may then become very violent. In addition, the presence of large quantities of molybdenum in the compound or compounds obtained (in general a mixture of oxides) involves serious disadvantages, either in subsequent damp treatments for the extraction of uranium, because of the untimely formation of molybdenum-based precipitates, or in separation by the distillation of fluorides, resulting from the fluoridation of the oxides, because of the very great similarity of properties between the fluorides of moylbdenum and uranium.

The present invention relates to a process for preparing compounds (or a compound) of uranium which are practically free from molybdenum, from uranium-molybdenum alloys. This preparation is carried out at moderate temperatures, and enables the molybdenum to be eliminated at the same time as the alloy is attacked.

The process according to the invention comprises treating a uranium-molybdenum alloy with a gaseous mixture of a hydrogen halide and an oxygen-containing gas, the alloy at least initially being at a temperature of from 100 to 300 C. in order to initiate the reaction between the gaseous mixture and the alloy and the product of the reaction constituting the desired compounds.

The reaction is preferably carried out with gaseous mixtures containing hydrochloric or hydrofluoric acid and oxygen. It may also be carried using hydriodic acid or hydrobromic acid as the hydrogen halide but these acids are less advantageous,-in particular because of their cost, and do not lead to an industrial process as economical as do hydrochloric and hydrofluoric acid.

The residue or product of the reaction has the advantage that it can be converted into substantially pure uranium hexafluoride (in particular free from moylbdenum) by fluoridizing and then distilling the product of the reaction.

Where the reaction is carried out with a gaseous mixture containing hydrochloric acid, the major part of the molybdenum present in the alloy is sublimated in the form of oxychloride, a little uranium is also carried away with the sublimate as uranium oxychloride is also very volatile. The uranium remains in the residue chiefly in the form of oxide.

In order to prepare substantially pure uranium hexafluoride as' mentioned above, this oxide may subsequently be fluoridized by any suitable method, such as the action of fluorine or an halogen fluoride.

This oxide may also subsequently be subjected to damp treatment in order to extract uranium by any suitable method based, for example, on the use of organic resins or solvents.

Where the gaseous mixture contains hydrofluoric acid, the molybdenum oxyfluoride formed is eliminated by vaporization, while the uranium remains in the residue in the form of a mixture of oxyfluoride and tetrafluoride.

This residue is particularly suitable for the production of uranium hexafluoride by fluoridation, since it already contains, in the combined state, about a third of the total quantity of fluorine present in the desired hexafluoride. The additional quantity of fluorine required can be introduced by using hydrofluoric acid, which is a much more economical reagent than fluorine. In addition, the fluoridation reaction starting from this intermediate mixture of uranium oxyfluoride and tetrafluoride is less exothermic and easier to control than the reaction starting from a uranium oxide and this also has the advantage of reducing corrosion of the equipment used.

In order that the invention may be more fully understood, some examples of the process will now be described, by way of illustration only, with reference to the accompanying diagrammatic drawings.

Referring to the drawings, FIGURES 1, 2, .3 and 4 diagrammatically illustrate the treatment of uraniummolybdenum alloys containing 0.5%, 1%, 2% and 10% of molybdenum respectively. The reactions were carried out in a horizontal stainless steel or Monel tube according to whether hydrochloric acid or hydrofluoric acid was used; the alloy to be treated was preferably in a subdivided state, for example in the form of granules. The reaction tube was placed inside an oven which was adjusted to give a temperature rise of C. per hour and the gaseous mixture used in the reaction was passed at a low rate from one end of the oven to the other, the gaseous mixture could instead have been introduced all at once for the whole duration of the reaction.

Each figure shows the curve a of temperature rise T of the alloy as a function of time'in the absence of the gaseous mixture, and the three curves b, c and d of temperature rise of the alloy as a function of time t expressed in hours, obtained respectively with a mixture of hydrochloric acid and oxygen, with a mixture of hydrofluoric acid and oxygen, with oxygen alone.

It will be seen that in all cases it is the reaction with oxygen alone which starts at the highest temperature and also that the reaction starts at a lower temperature with hydrofluoric acid than with hydrochloric acid; this starting temperature is below 200 C. with hydrofluoric acid and below 300 C. with hydrochloric acid. It will also be noted that the temperature rise as the reaction progresses is appreciably less with hydrofluoric acid than with hydrochloric acid.

The process can also be carried out with the oxidizing reaction starting only after the oven has been thermally balanced.

In the case of mixtures of hydrochloric acid and oxygen, it has been found that a reduction in the HCl/O ratio has the effect of increasing the rate of reaction. It has also been observed that the temperature rises from the instant when oxygen is admitted, while the temperature is not affected by the admission of hydrochloric acid without the admission of oxygen. The reaction is therefore readily controlled by simply adjusting the rate of oxygen delivery.

The rate of reaction always increases with temperature; thus, if the temperature is increased at the beginning'of the reaction by thermally balancing the oven at a higher temperature and if the foregoing ratio is allowed to remain constant, the rate of reaction is increased.

Whatever the thermal conditions envisaged, rates of reaction are much higher than those which would be obtained by the action of hydrochloric acid alone, which action would lead to the production of chlorides.

In the case of mixtures of hydrofluoric acid and oxygen, if the starting temperature of the reaction is varied while the HF/Og ratio is allowed to remain constant, the reaction speed is increased as in the case of hydrochloric acid.

On the other hand, the rate of reaction is practically unaffected by variation in the HF/O ratio, at least when the latter is between 0.5 and 10.

About 90% of the molybdenum contained in the alloy may be eliminated by this process (this corresponds, for the four above-mentioned alloys, to intermediate products having a Mo/U ratio of about 0.05%, 0.1%, 0.2% and 1% respectively), uranium loss in the course of the treatment is less than 0.5%.

The molecular ratio of hydrogen halide/oxygen should preferably be between 0.5 and 10, the optimum value being in the region of 2; with mixtures richer in oxygen, the reaction tends to start only at a high temperature (above 300 C.); with mixtures richer in hydrogen halide, more particularly in the case of the hydrochloric acidoxygen mixtures, the rate of reaction becomes too low.

It should also be noted that, without departing from the scope of the invention, one or more gaseous diluents may be present in the gaseous mixture containing hydrofluoric or hydrochloric acid and oxygen and the reaction with the alloy may thus be carried out with the oxygen replaced by air which may or may not be enriched in oxygen, the nitrogen enabling some'of the reaction heat to be removed. For good results, the maximum permissible quantity of nitrogen is of the order of 73% by volume: the introduction of nitrogen does not upset the limits of the hydrogen halide/oxygen ratio mentioned above.

What we claim is: 1

1. A process for preparing from uranium-molybdenum alloys a substantially molybdenum free residue of uranium compounds selected from the group consisting of uranium-oxyfluoride, uranium-tetrafluoride and uranium oxides, said process comprising the steps of initiating a reaction between said uranium-molybdenum alloy and a gaseous mixture comprising hydrofluoric acid and an oxygen-containing gas at a temperature of at least 100 C. but below 200 C. to eliminate said molybdenum as a volatile oxyhalide and recover a non-volatile uranium residue containing at least one of said uranium compounds and continuing said reaction until substantially all of said molybdenum has been eliminated.

2. A process as claimed in claim 1 wherein hydrogen halide is hydrofluoric acid and the molecular ratio of said hydrofluoric acid to oxygen in said gaseous mixture is between about 0.5 to 10, said uranium reaction product obtained thereby comprising uranium oxyfluoride and uranium fluoride.

3. A process as claimed in claim 1 wherein said gaseous mixture includes up to 73% by volume of nitrogen.

4. A process as claimed in claim 1 wherein said uranium reaction product is subsequently fluoridized and then distilled to thereby obtain substantially pure uranium hexafluoride.

5. A process as claimed in claim 1 wherein the temperature at which the reaction is initiated varies from about C. to C.

6. A process as claimed in claim 5 wherein the molar ratio of HF to O is 2/ 1.

References Cited by the Examiner UNITED STATES PATENTS 2,582,941 1/52 Wilder 23-145 2,859,096 11/58 Fowler 2314.5 2,865,704 12/58 Jaffey et al. 23-14.5 2,869,982 1/59 Brown et al. 2,887,356 5/59 Arnoflf 23-145 2,907,630 10/59 Lawroski ct al. 23l4.5 2,910,344 10/ 59 Davidson 2314.5 3,148,941 9/64 Gens 2314.5

OTHER REFERENCES Katz' et al.: The Chemistry of Uranium, part I, 1st edition, pp. 322, 323, 580, 581 (1951) QB l81.U7K3.

Kileifer et al.: Molybdenum Compounds, p. 62, Interscience Publishers (1952) QB 181 M7K5.

Nuclear Science Abstracts, vol. 15, abstract 17007 which reports an article by Speeckaert (Brussels, Centre dEtude de lEnergie Nucleaire) Sept. 1, 1960 and this date is relied on.

ORNL 3019, pp. 1, 4-21, May 12, 1961.

CARL D. QUARFORTH, Primary Examiner.

OSCAR R. VERTIZ, LEON D. ROSDOL, REUBEN EPSTEIN, Examiners. 

1. A PROCESS FOR PREPARING FROM URANIUM-MOLYBDENUM ALLOYS A SUBSTANTIALLY MOLYBDENUM FREE RESIDUE OF URANIUM COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF URANIUM-OXYFLUORIDE, URANIUM-TETRAFLUORIDE AND URANIUM OXIDES, SAID PROCESS COMPRISING THE STEPS OF INITIATING A REACTION BETWEEN SAID URANIUM-MOLYBDENUM ALLOY AND A GASEOUS MIXTURE COMPRISING HYDROFLUORIC ACID AND AN OXYGEN-CONTAINING GAS AT A TEMPERATURE OF AT LEAST 100*C. BUT BELOW 200*C. TO ELIMINATE SAID MOLYBDENUM AS A VOLATILE OXYHALIDE AND RECOVER A NON-VOLATILE URANIUM RESIDUE CONTAINING AT LEAST ONE OF SAID URANIUM COMPOUNDS AND CONTINUING SAID REACTION UNTIL SUBSTANTIALLY ALL OF SAID MOLYBDENUM HAS BEEN ELIMINATED. 